Abstract-Frequency‐Agile Temporal Terahertz Metamaterials

Prakash Pitchappa,   Abhishek Kumar,   Haidong Liang,   Saurav Prakash,   Nan Wang,   Andrew A. Bettiol,   Thirumalai Venkatesan,  Chengkuo Lee,   Ranjan Singh,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202000101

Spatiotemporal manipulation of electromagnetic waves has recently enabled a plethora of exotic optical functionalities, such as non‐reciprocity, dynamic wavefront control, unidirectional transmission, linear frequency conversion, and electromagnetic Doppler cloak. Here, an additional dimension is introduced for advanced manipulation of terahertz waves in the space‐time, and frequency domains through integration of spatially reconfigurable microelectromechanical systems and photoresponsive material into metamaterials. A large and continuous frequency agility is achieved through movable microcantilevers. The ultrafast resonance modulation occurs upon photoexcitation of ion‐irradiated silicon substrate that hosts the microcantilever metamaterial. The fabricated metamaterial switches in 400 ps and provides large spectral tunability of 250 GHz with 100% resonance modulation at each frequency. The integration of perfectly complementing technologies of microelectromechanical systems, femtosecond optical control and ion‐irradiated silicon provides unprecedented concurrent control over space, time, and frequency response of metamaterial for designing frequency‐agile spatiotemporal modulators, active beamforming, and low‐power frequency converters for the next generation terahertz wireless communications

Abstract-Excitons in 2D perovskites for ultrafast terahertz photonic devices

Abhishek Kumar,  Ankur Solanki,  Manukumara Manjappa,  Sankaran Ramesh,  Yogesh Kumar Srivastava, Piyush Agarwal,  Tze Chien Sum. Ranjan Singh

https://advances.sciencemag.org/content/6/8/eaax8821

In recent years, two-dimensional (2D) Ruddlesden-Popper perovskites have emerged as promising candidates for environmentally stable solar cells, highly efficient light-emitting diodes, and resistive memory devices. The remarkable existence of self-assembled quantum well (QW) structures in solution-processed 2D perovskites offers a diverse range of optoelectronic properties, which remain largely unexplored. Here, we experimentally observe ultrafast relaxation of free carriers in 20 ps due to the quantum confinement of free carriers in a self-assembled QW structures that form excitons. Furthermore, hybridizing the 2D perovskites with metamaterials on a rigid and a flexible substrate enables modulation of terahertz fields at 50-GHz modulating speed, which is the fastest for a solution-processed semiconductor-based photonic device. Hence, an exciton-based ultrafast response of 2D perovskites opens up large avenues for a wide range of scalable dynamic photonic devices with potential applications in flexible photonics, ultrafast wavefront control, and short-range wireless terahertz communications.

Abstract-Solution‐Processed Lead Iodide for Ultrafast All‐Optical Switching of Terahertz Photonic Devices

Manukumara Manjappa, Ankur Solanki, Abhishek Kumar,Tze Chien Sum, Ranjan Singh,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201901455


Solution‐processed lead iodide (PbI2) governs the charge transport characteristics in the hybrid metal halide perovskites. Besides being a precursor in enhancing the performance of perovskite solar cells, PbI2 alone offers remarkable optical and ultrasensitive photoresponsive properties that remain largely unexplored. Here, the photophysics and the ultrafast carrier dynamics of the solution processed PbI2 thin film is probed experimentally. A PbI2 integrated metamaterial photonic device with switchable picosecond time response at extremely low photoexcitation fluences is demonstrated. Further, findings show strongly confined terahertz field induced tailoring of sensitivity and switching time of the metamaterial resonances for different thicknesses of PbI2 thin film. The approach has two far reaching consequences: the first lead‐iodide‐based ultrafast photonic device and resonantly confined electromagnetic field tailored transient nonequilibrium dynamics of PbI2 which could also be applied to a broad range of semiconductors for designing on‐chip, ultrafast, all‐optical switchable photonic devices.

Abstract-Chalcogenide Phase Change Material for Active Terahertz Photonics

Prakash Pitchappa,  Abhishek Kumar,  Saurav Prakash,  Hariom Jani,
Thirumalai Venkatesan, Ranjan Sing,

https://onlinelibrary.wiley.com/doi/full/10.1002/adma.201808157

The strikingly contrasting optical properties of various phases of chalcogenide phase change materials (PCM) has recently led to the development of novel photonic devices such as all‐optical non‐von Neumann memory, nanopixel displays, color rendering, and reconfigurable nanoplasmonics. However, the exploration of chalcogenide photonics is currently limited to optical and infrared frequencies. Here, a phase change material integrated terahertz metamaterial for multilevel nonvolatile resonance switching with spatial and temporal selectivity is demonstrated. By controlling the crystalline proportion of the PCM film, multilevel, non‐volatile, terahertz resonance switching states with long retention time at zero hold power are realized. Spatially selective reconfiguration at sub‐metamaterial scale is shown by delivering electrical stimulus locally through designer interconnect architecture. The PCM metamaterial also features ultrafast optical modulation of terahertz resonances with tunable switching speed based on the crystalline order of the PCM film. The multilevel nonvolatile, spatially selective, and temporally tunable PCM metamaterial will provide a pathway toward development of novel and disruptive terahertz technologies including spatio‐temporal terahertz modulators for high speed wireless communication, neuromorphic photonics, and machine‐learning metamaterials.

Abstract-Phase change-photonic framework for terahertz wave control

Prakash Pitchappa, Abhishek Kumar, Saurav Prakash, Hariom Jani, Thirumalai Venkatesan, Ranjan Singh

https://arxiv.org/abs/1811.02729

The advancement in capabilities enabled by handheld devices and the prospective internet of things has led to an explosion of wireless data consumption in the last decade. The ever-increasing demand for high speed data transfer has projected the unprecedented importance of terahertz spectral range for next generation wireless communication systems. However, versatile interaction and active manipulation of terahertz waves required for a wide-range of terahertz technologies are either unavailable or unscalable. Here, we report on an integrated platform of chalcogenide phase change material, germanium antimony telluride (GST), with metamaterials for multidimensional manipulation of terahertz waves. The thermal, electrical and optical stimulation of GST provide multilevel non-volatility, sub-wavelength spatial selectivity and variable ultrafast switching of terahertz waves, respectively. These multifaceted response of phase change material can be used in tandem with metamaterial that enables strong field confinement along with on-demand spectral response and frequency selectivity. The unique and multifarious properties of GST combined with the versatility and scalability of metamaterial design and ease of fabrication could aid in the development of advanced devices operating in terahertz range, such as spatio-temporal light modulators, neuromorphic photonic devices, compressive imagers, and switchable holograms, vital for the next generation wireless communication systems.

Abstract-Color‐Sensitive Ultrafast Optical Modulation and Switching of Terahertz Plasmonic Devices

Abhishek Kumar,   Yogesh Kumar,  Srivastava  Manukumara,  Manjappa, Ranjan Singh


https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201800030

2D micro‐nanostructured metal films with hole arrays show promising features such as the extraordinary transmission of light. Such systems are interesting in the field of subwavelength photonics and nonlinear optics due to their high field confinement in addition to their inherent spectral scalability and frequency selective response. Several active schemes to control the extraordinary transmission are recently demonstrated. However, these dynamic devices do not reveal any obvious color‐dependent modulation of the resonant transmission behavior. Here, color‐sensitive ultrafast modulation of extraordinary resonant transmission of terahertz (THz) waves through 2D metallic hole arrays is demonstrated. Pumping the silicon beneath the metallic array with light of different colors and identical fluences exhibit significantly different ultrafast switching dynamics and modulation. The color‐dependent sensitivity and control of THz waves at an ultrafast timescale provide an extra degree of freedom that opens up new opportunities for future applications in active subwavelength optics, optoelectronics, and all‐optical switching of THz photonic devices.

Abstract-Hybrid Lead Halide Perovskites for Ultrasensitive Photoactive Switching in Terahertz Metamaterial Devices

Manukumara Manjappa, Yogesh Kumar Srivastava, Ankur Solanki, Abhishek Kumar, Tze Chien Sum, Ranjan Singh

http://onlinelibrary.wiley.com/doi/10.1002/adma.201605881/abstract

The recent meteoric rise in the field of photovoltaics with the discovery of highly efficient solar-cell devices is inspired by solution-processed organic–inorganic lead halide perovskites that exhibit unprecedented light-to-electricity conversion efficiencies. The stunning performance of perovskites is attributed to their strong photoresponsive properties that are thoroughly utilized in designing excellent perovskite solar cells, light-emitting diodes, infrared lasers, and ultrafast photodetectors. However, optoelectronic application of halide perovskites in realizing highly efficient subwavelength photonic devices has remained a challenge. Here, the remarkable photoconductivity of organic–inorganic lead halide perovskites is exploited to demonstrate a hybrid perovskite–metamaterial device that shows extremely low power photoswitching of the metamaterial resonances in the terahertz part of the electromagnetic spectrum. Furthermore, a signature of a coupled phonon–metamaterial resonance is observed at higher pump powers, where the Fano resonance amplitude is extremely weak. In addition, a low threshold, dynamic control of the highly confined electric field intensity is also observed in the system, which could tremendously benefit the new generation of subwavelength photonic devices as active sensors, low threshold optically controlled lasers, and active nonlinear devices with enhanced functionalities in the infrared, optical, and the terahertz parts of the electromagnetic spectrum.